Wireless devices of many types including cellular telephones, laptop computers, tablet computers and so forth, typically include a separate semiconductor device called a power amplifier (PA) that is configured to receive a radio frequency (RF) signal from a radio transceiver and amplify the power of the RF signal so that it can be radiated out of the system via a load such as a given antenna to enable wireless communication to occur. The transceiver receives various signals from a baseband processor of the system, which processes the transmitted and received data as well as controls various functions of the radio.
As newer wireless communication standards begin to be adopted, greater control of operation is needed to meet various performance requirements. In addition, it is desirable to optimize performance of a PA for various reasons, including improved fidelity of communications as well as reducing power consumption.
For WCDMA and LTE RF power amplifiers it is desired to optimize the PA performance (linearity and efficiency). This is becoming more difficult as new technologies such as average power tracking (APT) and envelope tracking (ET) are deployed with tighter tolerances in order to meet specifications. In APT, the supply voltage of the power amplifier changes depending on the output power control signal which changes significantly slower than the modulation rate. When the supply voltage changes, it tends to change tuning, linearity and other parameters of the PA. With ET, the power supply of the PA tracks the envelope of the RF signal, so that the supply changes faster than the modulation rate. As such additional constraints are imposed on the power amplifier in that, as voltage changes, it is desirable to limit gain and phase changes. Traditionally PA control has been done using simple analog circuitry methods.